1. Field of the Invention
The present invention relates to an apparatus (cuvette) for taking up and storing liquids and for carrying out optical measurements
2. Description of the Background of the Invention
In vitro diagnostic methods are increasingly characterized by automation of the tests and measurement procedures to be carried out. The background to this requirement comprises, on the one hand, the desire to exclude individual factors in the manipulation and carrying out by any operating staff and, on the other hand, the increasingly high costs associated with use of staff.
The development and carrying out of chemical methods of protein measurement in automated laboratory operation thus make great demands on the knowledge of the technical procedure and quality assurance.
The growing demands on the specificity and sensitivity of the tests and the simultaneous requirement for greater output by an analyzer therefore make it necessary to extend previous concepts of the manipulation of liquids. To carry out a chemical test for proteins, as a rule two types of liquid starting components are required: the sample obtained from the patient to be investigated, and the reagent components necessary for the diagnostic result.
While the sample comprises, after any necessary preparative steps (centrifugation, removal of cellular constituents or the like) have been carried out, only one component, the reagent is frequently composed of several constituents.
In the technical procedure for a diagnostic test, the sample and the test components must frequently be taken up in a particular sequence. With most analyzers, this is effected by a pipetting apparatus which carries out these steps successively or else combined in a suitable way. Between the individual tests, the parts of the pipetting apparatus coming into contact with the liquid, such as the inside and outside of the needle, are washed by a suitable cleaning solution so that they are available again without contaminated portions to take up the following sample or test liquids. Similar processes are carried out to clean reusable reaction vessels.
This process described above is thus suitable for continuous and automatic operation as long as the requirements for the cleaning conditions and the quality of the cleaning process are sufficiently consistent such that there are no measurable effects on a subsequent test due to constituents which may be bound by adsorption to the surface, or they can be precluded by other quality assurance measures in the test.
Unfortunately, many of the more recent diagnostic tests, such as the range of tumor markers or microbiological tests, now have no firmly defined diagnostically relevant region of measurement. In the case of tumor markers, it is necessary to determine all values above a particular threshold, and in microbiology it is necessary to be able to measure down to the region of a few molecules.
These requirements, therefore, frequently no longer permit the components coming into contact with the liquids to be cleaned by repeated washing without additional measures. In addition, traces of constituents of the cleaning solution remaining on the surface might themselves lead to irreversible falsification of the result. On the other hand, as the requirements increase there is a very large increase in the consumption of and thus the costs of cleaning solution. Measures to improve the cleaning, while at the same time reducing consumption require additional apparatus measures (heating the cleaning solution, source of ultrasound or the like).
In order to avoid all these difficulties, many suppliers of diagnostic analytical systems therefore already offer disposable articles for pipette tips and for reaction vessels. Another approach is to use ready-packaged test modules. In this case, the necessary constituents of the reagent are prepared so that it is now necessary only to add a sample and mix the reagent components.
The disadvantage of the last-mentioned process is the provision of the test components for the individual test, their preservation and storage inside and outside the analyzer. These measures can usually be implemented only at considerably more cost than removal of the test liquid from larger storage bottles. The technical procedure for tests in an analyzer usually entails separate transfer of liquids and provision of reaction vessels. In this case, the liquids are transferred by metering systems, which are coupled to movable units (X-Y-Z transfer arms), to the location of the reaction vessel when, possibly after further incubation steps, the reaction fluid present in the vessel is measured.
Thus, prior art analyzers involve use both of disposable articles for the metering in the form of exchangeable tips and of disposable articles as reaction vessels which are fed on demand continuously to a processing unit.
This procedure makes it possible to carry out measurements completely without carryover, it being necessary to use at least one exchangeable tip and one reaction vessel per analytical result. This results in a considerable contribution to the overall cost by consumables, which may be of the order of DM 0.05-0.30 per consumable article in the case of disposable articles suitable for automated equipment. In addition, the individual consumable articles must be processed inside the automatic analyzer. The taking up of the exchangeable tip, the liquid transfer and the discarding of the used tip on the one hand, and the feeding of disposable reaction vessels mean that a large number of electromechanical actuation units are required. The entire technical procedure is thus very time consuming. This has direct effects on the speed and the output of an automatic analyzer.